1. Field of the Invention
The present invention relates to an objective lens system for use in a single lens reflex camera, and more particularly, to an improved compact Gauss type lens system of five units and six lens elements.
2. Description of the Prior Art
Numerous attempts have been made in the prior art to improve Gauss type lens systems for single lens reflex cameras. Recently, the demands of the consuming public have required smaller and more compact lightweight single reflex cameras. Attempts have been made to provide five lens units, six lens elements systems of a compact configuration, such as U.S. Pat. Nos. 4,131,335 and 3,817,603. Additional examples are shown in Japanese Patent publication No. 38-11587, and Japanese Laid-Open Patent application Nos. 52-114322, 49-53419, 52-108426, 52- 146620, 53-110822, 53-131034, 54-104334 and 54-156629.
As can be readily determined, the prior art is relatively crowded. Some of these prior art Gauss type lens systems are constructed of relatively economical glass material of low refractive indices and provide a relatively long back focal length. There have been problems, however, in shortening the total length of the lens system to meet the requirements of compactness and lightness in weight. Attempts to satisfy these conflicting design parameters have been made with the use of a relatively expensive glass material of relatively high refractive indices.
As can be readily appreciated, the rigors of competition in the camera industry forces a lens manufacturer to be acutely aware of the cost competitiveness of his product. There is a demand in the photography field to provide an improved Gauss type lens system of a five lens unit, six lens element that provides an adequate back focal length while shortening the total length of the lens system with the use of a relatively economical glass material while of course providing proper correction of aberrations.